1. Field of the Invention
The invention relates to a pump that sucks in and discharges fluid such as oil.
2. Description of the Related Art
As described in Japanese Patent Application Publication No. 11-324938 (JP 11-324938 A), an oil pump used in an automobile includes an outer rotor, an inner rotor and a housing having a pump chamber in which the outer rotor and the inner rotor are rotatably accommodated. Internal teeth formed in a trochoidal curve shape are formed on the inner periphery of the outer rotor. External teeth formed in a trochoidal curve shape are formed on the outer periphery of the inner rotor, and meshed with the internal teeth of the outer rotor. The inner rotor is rotated by a motor.
The housing has a suction passage and a discharge passage that are communicated with the pump chamber. The pump chamber of the housing has a bottom portion in which a suction-side groove communicated with the suction passage and a discharge-side groove communicated with the discharge passage are formed as recesses. The suction-side groove and the discharge-side groove are apart from each other and extend along the circumferential direction of the bottom portion of the pump chamber. In the oil pump configured as described above, the inner rotor and the outer rotor rotate while being meshed with each other. Thus, the oil sucked in through the suction passage is discharged through the discharge passage.
In some conventional pumps, an inner edge of a discharge-side groove is located radially outward of the bottom lands of external teeth of an inner rotor. This is because, if the length of contact between the inner rotor and a bottom portion of a pump chamber in the radial direction is set longer, it is possible to suppress leakage of the oil from spaces defined between the external teeth and the internal teeth into a side clearance that is a clearance between the bottom portion of the pump chamber and the inner rotor, thereby enhancing the efficiency of the pump.
If the inner edge of the discharge-side groove is located radially outward of the bottom lands of the external teeth of the inner rotor, the tooth tips of the internal teeth may be overlapped with the inner edge of the discharge-side groove. In this case, the spaces defined between the external teeth and the internal teeth are turned into closed spaces that are not opened into the discharge-side groove. When the volumes of the closed spaces are decreased as the inner rotor and the outer rotor rotate, the oil in the closed spaces flows at a high flow rate into spaces between the internal teeth and the external teeth, which are opened into the discharge-side groove. This raises a possibility that the inner edge of the discharge-side groove will be damaged.